1. Field of the Invention
The present invention relates in general to the broad area of sensing mediums and more specifically to a sensing medium that includes a plurality of layers of electret material as sensing elements that may be employed to provide temperature compensation.
2. Description of the Prior Art
One common definition of an electret is a dielectric material permanently polarized by heating the material and placing it in a strong electric field during cooling. Electrets are commonly classified on the basis of pyroelectric or piezoelectric properties, both of which produce an electrical signal due to a change in dipole moment. Although pyroelectric and piezoelectric materials are often thought of as two distinct classes of electrets, actually piezoelectric materials are a generic class in which pyroelectric materials are included as a species. Thus, a large number of materials have both pyroelectric and piezoelectric characteristics.
Several temperature compensated detectors that employ pyroelectric sensing mediums are described in a U.S. Pat. to McHenry, No. 3,453,432, and in my co-pending application Ser. No. 430,055, filed Jan. 2, 1974 and entitled "Pyroelectic Temperature Compensated Sensing Apparatus now U.S. Pat. No. 3,877,308, issued Apr. 15, 1975. Although such known detectors provide heat sensing detection that is temperature compensated, none of these earlier detectors disclose a sensing medium that can be conveniently manufactured in a continuous configuration in tape form.
The present invention provides a sensing medium that may be readily constructed in tape form in order to facilitate its use in a wide variety of applications.